Atomic layer deposition of metal carbide films using aluminum hydrocarbon compounds

ABSTRACT

Methods of forming metal carbide films are provided. In some embodiments, a substrate is exposed to alternating pulses of a transition metal species and an aluminum hydrocarbon compound, such as TMA, DMAH, or TEA. The aluminum hydrocarbon compound is selected to achieve the desired properties of the metal carbide film, such as aluminum concentration, resistivity, adhesion and oxidation resistance. In some embodiments, the methods are used to form a metal carbide layer that determines the work function of a control gate in a flash memory.

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. application Ser. No.12/424,470, filed Apr. 15, 2009, now abandoned, which claims priorityunder 35 U.S.C. §119(e) to U.S. provisional application No. 61/045,554,filed Apr. 16, 2008, each of which is hereby incorporated by referencein its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates generally to vapor deposition processesand, more particularly, to deposition of metal carbide films by vapordeposition processes.

Description of the Related Art

Metal carbides have found use in various applications in the electronicsindustry, from gate electrodes to diffusion barriers. For example,tantalum carbide (TaC) is a low resistivity metal that can be used as ann-type metal oxide semiconductor (NMOS) gate electrode. Further, TaC hasbeen found to be effective at inhibiting electromigration of noble metalatoms at the interface between metal interconnects and metal lines.

Generally, carbides of transition metal elements are in groups 4, 5, 6,7, 8, 9, and 11 of the periodic table. Transition metal carbides arerelatively inert, have very high melting points, are extremely hard andwear resistant, and have high thermal conductivity and metal-likeelectrical conductivity.

Transition metal carbides can have a wide range of compositions. Orderedand disordered carbon deficient forms exist, of which the tungstencarbides, WC_(x), are examples. In these forms, carbon resides in theinterstitial cavities between metal atoms.

Metal carbide films have been formed by various methods includingchemical vapor deposition (CVD), physical vapor deposition (PVD) andatomic layer deposition (ALD).

A “thermal” ALD method of forming metal carbide films, wherein thesubstrate is sequentially and alternately contacted with vapor phasepulses of two or more source chemicals, is described in, for example,U.S. Pat. No. 6,482,262. According to the methods described therein, atransition metal source chemical and carbon source gas are alternatelyand sequentially pulsed into a reaction space comprising a substrate,which is maintained at an elevated temperature. The pulsing sequence isrepeated to form a metal carbide (e.g., TaC) film of desired thickness.Due to the self-limiting nature of ALD, films are grown at rate of aboutone monolayer (ML) per deposition cycle.

A CVD method of depositing tungsten carbide from tungsten hexafluoride,hydrogen and a carbon-containing gas has been described in, for example,international patent application WO 00/47796. The carbon-containingcompound is initially thermally activated. All of the gaseous sourcechemicals are introduced into a reaction space at the same time,resulting in the deposition of nonvolatile tungsten carbide on thesubstrate. A CVD reaction of WF₆ with trimethylamine and H₂ has beendisclosed to yield WC films at 700° C.-800° C. and beta-WC_(x) films at400° C.-600° C. (Nakajima et al., J. Electrochem. Soc. 144 (1997)2096-2100). The H₂ flow rate was found to affect the deposition rate ofthe tungsten carbide films. A problem with the disclosed process is thatthe substrate temperature is rather high relative to thermal budgets forstate-of-the-art semiconductor fabrication, particularly inmetallization stages.

PVD processes generally deposit along a line-of-sight. One method ofdepositing tantalum carbide for a diffusion barrier layer by PVD hasbeen described in U.S. Pat. No. 5,973,400. A tantalum carbide layer wasformed by sputtering tantalum or tantalum carbide under an N₂/CH₄/Aratmosphere. Line-of-sight deposition, however, means that complexsubstrate contours will have insufficient film coverage in shaded areas.Additionally, line-of-sight deposition means that low-volatility sourcematerial arriving directly from the source to the substrate will likelyadhere to the first solid surface that it encounters, thus producinglow-conformality coverage.

SUMMARY OF THE INVENTION

According to one aspect of the invention, methods for growing a metalcarbide film over a substrate are provided. The methods generallycomprise contacting a substrate in a reaction space with a firstreactant that includes a metal source chemical and a second reactantthat includes an aluminum hydrocarbon compound, thereby forming themetal carbide film over the substrate. The metal carbide film preferablycomprises aluminum.

According to some embodiments of the invention, atomic layer deposition(ALD) processes for forming a metal carbide thin film on a substrate ina reaction space are provided. The methods comprising: alternately andsequentially contacting the substrate with vapor phase pulses of a firstmetal precursor and a first aluminum hydrocarbon compound, such that ametal carbide film comprising from about 6 to about 16% aluminum isformed. In some embodiments the aluminum hydrocarbon compound comprisesone or more of trimethyl aluminum (TMA), triethyl aluminum (TEA), anddimethylaluminumhydride (DMAH).

In another aspect of the invention, metal carbide film comprisingaluminum are deposited using aluminum hydrocarbon compounds. The amountof the aluminum can be controlled by selecting an appropriate aluminumhydrocarbon compound as the second reactant. Other reaction conditions,such as temperature pressure, pulse and purge length and plasma, canalso be adjusted to achieve a desired aluminum concentration. In someembodiments the aluminum concentration is about 6%. In other embodimentsthe aluminum concentration is up to about 16%. However, higherconcentrations are possible. By controlling the amount of aluminum,films with desirable characteristics can be formed, including lowresistivity, good adhesion, and oxidation resistance.

In some embodiments, the resistivity of the metal carbide film iscontrolled by selecting appropriate deposition conditions, including thealuminum hydrocarbon reactant, the deposition temperature and thedeposition pressure.

In another aspect of the invention, methods of making metal carbideswith good adhesion properties are provided. In some embodiments,tantalum carbide films are deposited by ALD using tantalum halideprecursors and TEA.

In other embodiments, the oxidation resistance of a metal carbide filmis controlled by controlling the amount of aluminum in the metal carbidefilm. The amount of aluminum can be controlled by selection of analuminum hydrocarbon reactant for use in an ALD process as a carburizingagent and by adjusting other reaction conditions.

In some embodiments methods of forming a metal carbide thin film with adesired level of oxidation resistance are provided. The methodscomprise: depositing a metal carbide thin film by alternately andsequentially contacting a substrate with vapor phase pulses of a metalprecursor and an aluminum hydrocarbon compound, wherein one or morereaction conditions are selected to produce a desired concentration ofaluminum in the metal carbide thin film, and wherein the concentrationof aluminum in the metal carbide is from about 1 to about 30%.

In other embodiments, the work function of a gate electrode isdetermined by controlling the amount of aluminum in a metal carbidefilm. The gate electrode may be, for example, a control gate in a flashmemory structure or a gate electrode in a CMOS transistor. A gate stackcan comprise a first gate electrode layer and a second gate electrodelayer. The first gate electrode layer comprises a first metal carbidegate electrode material and the second gate electrode layer comprises asecond gate electrode material, such as polysilicon, titanium ortantalum nitride or tungsten. Preferably the first and second gateelectrode materials are conductive. In preferred embodiments, the firstgate electrode material is different from the second gate electrodematerial. The work function of the gate electrode may be determined bythe first metal carbide gate electrode material.

Methods for forming a flash memory comprising a metal carbide layer arealso provided. In preferred embodiments a dielectric layer (tunneloxide) is deposited over a substrate and a floating gate is depositeddirectly over the dielectric layer. The floating gate may comprise, forexample, polysilicon. In some embodiments, such as for a TaNOS flashstructure, a charge trap layer is used in place of the floating gate.The charge trap layer may be silicon nitride. A barrier oxide, such asAlO₂, is deposited over the floating gate or charge trap layer and acontrol gate is formed over the barrier oxide.

In some embodiments the methods for forming a flash memory on asubstrate comprise: forming a dielectric layer on the substrate; forminga charge trap layer directly over and adjacent to the dielectric layer;forming a barrier oxide directly over and adjacent to the charge traplayer: forming a metal carbide control gate over the barrier oxide;etching the dielectric layer, charge trap layer, barrier oxide andcontrol gate to form a flash structure; and passivating the flashstructure by depositing SiO₂, wherein the metal carbide control gatecomprises aluminum and during the deposition of SiO₂ the aluminum in themetal carbide reacts with oxygen to self-passivate the control gate.

Forming the control gate preferably comprises depositing a metal carbidegate electrode layer by ALD using one or more aluminum hydrocarboncompounds, such that the metal carbide layer controls the work functionof the control gate. The metal carbide layer is preferably deposited toa thickness of about 1 to 1000 Å, more preferably about 1 to 500 Å, andstill more preferably about 25 to 200 Å. The deposition conditions,including temperature, pressure and reactant choice are adjusted toachieve a desired amount of aluminum in the metal carbide layer and thusproduce the desired work function and other characteristics. Forexample, the aluminum content is preferably such that the film has goodoxidation resistance and is able to self-passivate during subsequentpatterning and/or deposition steps.

A further conductive layer, such as a polysilicon, metal or metalnitride layer, for example a titanium nitride or tungsten layer, may bedeposited over the first gate electrode layer. The structure is thenpatterned, etched and passivated, for example with silicon oxide. Duringthe passivation process, the edges of the metal carbide layer areexposed and the aluminum in the metal carbide reacts with oxygen toself-passivate the remaining metal film.

All of these embodiments are intended to be within the scope of theinvention herein disclosed. These and other embodiments of the presentinvention will be readily apparent to those skilled in the art from thefollowing detailed description of the preferred embodiments havingreference to the attached figure, the invention not being limited to anyparticular preferred embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from the Detailed Description ofthe Preferred Embodiments and from the appended drawing, which is meantto illustrate and not to limit the invention, and wherein:

FIG. 1 is a block diagram of a pulsing sequence in an ALD-type processaccording to some embodiment.

FIG. 2 is a schematic illustration of a flash memory structure formedaccording to some embodiments.

FIG. 3 is a schematic illustration of a gate electrode stack in a CMOStransistor.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

Metal carbide films, e.g., tantalum carbide (TaC) films, can be used toform various structures, such as control electrodes for flash memorystructures. In such applications, it is desirable for the films to havegood adhesion to underlying materials and also low resistivity and goodoxidation resistance.

Metal carbide films with desirable properties can be formed by employingaluminum hydrocarbon compounds to carburize a metal film on a substrate.In some embodiments of the present invention, metal carbide films areformed over a substrate in ALD-type processes by contacting thesubstrate with alternating and sequential pulses of a metal compound anda carbon-containing compound, where the carbon containing compound is analuminum hydrocarbon compound.

Using the methods and compositions described herein, metal carbide filmswith a controlled aluminum content can be formed on a substrate. Asubstrate in a reaction space is contacted with a vapor phase metalsource chemical (or metal compound) and an aluminum hydrocarboncompound. The films preferably have good adhesion, low resistivity andgood oxidation resistance. The characteristics of the metal carbidefilms including aluminum content, adhesion, resistivity and/or oxidationresistance can be controlled by selecting the appropriate aluminumhydrocarbon reactant. The reaction conditions, such as the reactiontemperature, pressure, pulse and purge times, pulsing sequence and postdeposition annealing can also be adjusted to achieve films with thedesired properties. In some embodiments, the desired filmcharacteristics may be achieved by using a plasma enhanced ALD process.

By selecting an appropriate aluminum hydrocarbon compound andappropriate reaction conditions, a metal carbide film with propertiesthat are advantageous to a particular situation can be formed. Forexample, in some embodiments a film with low resistivity is formed usingTMA, TEA or DMAH as the aluminum hydrocarbon compound. Films with goodadhesion can be obtained in some embodiments using TEA and a metalhalide reactant, such as TaCl₅. Oxidation resistant films can be formedin some embodiments by selecting reactants and conditions that provide adesired level of aluminum in a metal carbide film. For example, in someembodiments films with an aluminum concentration of about 1-30%, morepreferably about 6-16% are deposited in order to obtain a desired levelof oxidation resistance.

Although described herein primarily in the context of flash memoryapplications, the metal carbide films and deposition processes can finduse in a variety of contexts, as will be recognized by the skilledartisan. For example, the metal carbide film formed can be a componentof an integrated circuit (IC), such as, e.g., a conductive diffusionbarrier forming a part of a line in a dual damascene structure, a metalgate electrode in a CMOS transistor, such as an NMOS or PMOS gateelectrode (depending on the aluminum concentration), or ananti-reflective coating. In other embodiments, the metal carbide filmmay form a part of hard coating on a substrate to protect againstmechanical wear, or may be used as a component of a corrosion protectionlayer. In still other embodiments, the metal carbide film can be, e.g.,used as part of a chemical reaction catalyst or as an etch stop barrier.

DEFINITIONS

In context of the present disclosure, an “ALD process” or “ALD typeprocess” generally refers to a process for producing a film over asubstrate monolayer (molecular layer) by monolayer using self-saturatingchemical reactions. The general principles of ALD are disclosed, e.g.,in T. Suntola in, e.g. the Handbook of Crystal Growth 3, Thin Films andEpitaxy, Part B: Growth Mechanisms and Dynamics, Chapter 14, AtomicLayer Epitaxy, pp. 601-663, Elsevier Science B.V. 1994, and U.S. Pat.Nos. 4,058,430 and 5,711,811, the disclosures of which are incorporatedherein by reference. In an ALD process, gaseous reactants, i.e.,precursors or source materials are alternately and sequentiallyconducted into a reaction space where they contact a substrate toprovide a surface reaction. Reaction conditions are selected such thatgenerally only up to about one monolayer (i.e. an atomic layer or amolecular layer) of material is deposited at a time during each pulsingcycle. Gas phase reactions between precursors and any undesiredreactions of byproducts are inhibited because precursor pulses areseparated from each other and the reaction chamber is purged with aninactive gas (e.g. nitrogen, argon, or hydrogen) and/or evacuated using,e.g., a pumping system between precursor pulses to remove surplusgaseous reactants and reaction byproducts, if any, from the chamber.Thus, the concentration profiles of the reactants in the reaction spacewith respect to time are not overlapping. However, the skilled artisanwill recognize that more than one monolayer may be deposited in one ormore ALD cycles despite the separation of reactant pulses.

“Plasma-excited species” refers to radicals, ions or other excitedspecies generated via application of energy to a gas. Plasma-excitedspecies may be generated using a direct plasma generator (i.e., “insitu” or “direct” plasma generation) and/or a remote plasma generator(i.e., “ex situ” or “remote” plasma generation). Energy may be applied(or coupled) to a gas via a variety of methods, such as inductivecoupling, ultraviolet radiation, microwaves, capacitive coupling,application of RF power, etc. In the absence of coupling energy, plasmageneration is terminated. Plasma-excited species include, withoutlimitation, hydrogen and nitrogen radicals.

“Plasma parameters” is used to designate one or more plasma generationvariables, including, without limitation, plasma generator power, gaspressure, gas (or reactant) flow rate, and plasma pulse duration. As anexample, for plasma generation using RF power, plasma parametersinclude, without limitation, radio frequency (RF) power on time, RFpower amplitude, RF power frequency or frequencies (for dual frequencysystems), reactant concentration, reactant flow rate, reaction spacepressure, total gas flow rate, reactant pulse durations and separations,and RF electrode spacing.

“Reaction space” is used to designate a reactor or reaction chamber(“chamber”), or an arbitrarily defined volume therein, in whichconditions can be adjusted to effect film growth. The reaction space canbe, for example, in a single-wafer ALD reactor or a batch ALD reactor,where deposition on multiple substrates takes place at the same time.

“Adsorption” is used to designate a chemical attachment of atoms ormolecules on a surface.

“Substrate” is any surface on which deposition is desired, and inpreferred embodiments can include any workpiece that is suitable forintegrated circuit (IC) fabrication. Typical substrates include, withoutlimitation, silicon, silica, coated silicon and high k materials, suchas metal oxides.

“Surface” is used to designate a boundary between the reaction space anda feature of the substrate.

“Film” means a film that is grown on a substrate from elements orcompounds that are transported as separate ions, atoms or molecules froma source to the substrate. The thickness of the film will depend uponthe application and may vary in a wide range, preferably from one atomiclayer to 100 nanometers (nm) or more. In some embodiments, such as wherethe film serves to set the work function in a flash memory, thethickness may be about 25 Å to 200 Å, although in some embodiments itmay be as high as 500 Å or even 1000 Å. In other embodiments the film isless than about 200 Å in thickness, even more preferably less than about100 Å, and most preferably less than about 50 Å, such as for a CMOS gateapplication.

“Metal carbide film” designates a film comprising at least one metal andcarbon. The metal may be a single elemental metal or a plurality ofmetals, such as a metal alloy. The metal carbide film may bestoichiometric, e.g., TaC, or non-stoichiometric, e.g., TaC_(x), where‘x’ is greater than one if the film has excess carbon or less than oneif the film is carbon deficient. In preferred embodiments, metal carbidefilms deposited according to the methods described herein comprise afirst metal, carbon, and aluminum. The first metal is typically notaluminum.

ALD Methods

ALD is based on self-limiting reactions, whereby sequential andalternating pulses of reaction precursors are used to deposit about oneatomic (or molecular) monolayer of material per deposition pulse. Thedeposition conditions and precursors are selected to provideself-saturating reactions, such that an adsorbed layer in one pulseleaves a surface termination that is non-reactive with the gas phasereactants of the same pulse. A subsequent pulse of different reactantsreacts with the previous termination to enable continued deposition.Thus, each cycle of alternated pulses typically leaves no more thanabout one monolayer of the desired material. However, as mentionedabove, the skilled artisan will recognize that in one or more ALD cyclesmore than one monolayer of material may be deposited, for example ifsome gas phase reactions occur despite separate provisions of thereactants.

In a typical ALD-type process for depositing metal carbide films, onedeposition cycle comprises exposing the substrate to a first reactant,removing any unreacted first reactant and reaction byproducts from thereaction space, exposing the substrate to a second reactant, followed bya second removal step. The first reactant is preferably a metalprecursor and the second reactant is preferably a carburizing (orcarbon-contributing) compound (although it is possible to begin theprocess with either reactant).

The metal compound preferably comprises one or more metals selected fromthe group consisting of titanium (Ti), zirconium (Zr), hafnium (Hf),vanadium (V), niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum(Mo), tungsten (W), manganese (Mn), rhenium (Re), iron (Fe), cobalt(Co), nickel (Ni), copper (Cu), silver (Ag), gold (Au), palladium (Pd),platinum (Pt), rhodium (Rh), iridium (Ir), ruthenium (Ru) and osmium(Os).

Typically, halide reactants, such as, e.g., TaCl₅ and HfCl₄, are used asmetal precursors in ALD deposition because these precursors areinexpensive and relatively stable, but at the same time reactive towardsdifferent types of surface groups.

Carbon-contributing compounds are preferably aluminum hydrocarboncompounds. The aluminum hydrocarbon compound may be, for example, analkane, alkene or alkyne. In some embodiments the aluminum hydrocarboncompound is selected from the group consisting of trimethyl aluminum(TMA), triethyl aluminum (TEA) and dimethylaluminumhydride (DMAH).

The aluminum hydrocarbon compound is preferably selected to achievedesired characteristics in the metal carbide film. These include,without limitation, adhesion, resistivity, oxidation resistance and workfunction. In addition, by selecting an appropriate aluminum hydrocarboncompound and appropriate deposition conditions, the level of aluminum inthe metal carbide film can be controlled. For example, to achieve ahigher aluminum concentration in a particular film, TEA may be selectedover TMA. In some embodiments, different aluminum hydrocarbon compoundsmay be used in different ALD deposition cycles to modify the aluminumincorporation in the metal carbide film. For example, in a depositionprocess to deposit a metal carbide layer a first ALD cycle may use afirst aluminum compound and one or more ALD cycles may use a differentaluminum compound.

The separation of precursors by inert gases, such as Ar, preventsgas-phase reactions between reactants and enables self-saturatingsurface reactions. Because the reactions self-saturate, stricttemperature control of the substrates and precise dosage control of theprecursors is not required. However, the substrate temperature ispreferably such that an incident gas species does not condense intomonolayers nor decompose on the surface. Surplus chemicals and reactionbyproducts, if any, are removed from the reaction space before the nextreactive chemical pulse is introduced into the chamber. Undesiredgaseous molecules can be effectively expelled from the reaction spacewith the help of an inert purging gas. The purging gas directs thesuperfluous molecules out of the chamber. A vacuum pump may be used toassist in the purging.

According to some embodiments of the invention, an ALD-type process isused to form metal carbide films on a substrate, such as an integratedcircuit workpiece. Preferably, each ALD cycle comprises two distinctdeposition steps or phases. In a first phase of the deposition cycle(“the metal phase”), a first reactant comprising a metal (i.e., metalsource material or chemical) is pulsed to the reaction space andchemisorbs onto the substrate surface, forming no more than about onemonolayer on the surface of the substrate. The metal source material inthis phase is selected such that, under the preferred conditions, theamount of metal source material that can be bound to the surface isdetermined by the number of available binding sites and by the physicalsize of the chemisorbed species (including ligands). The chemisorbedlayer left by a pulse of the metal source chemical is self-terminatedwith a surface that is non-reactive with the remaining chemistry of thatpulse. This phenomenon is referred to herein as “self-saturation.” Oneof skill in the art will recognize that the self-limiting nature of thisphase makes the entire ALD cycle self-limiting.

The metal source material preferably includes a metal species desired inthe film being deposited. In some embodiments, the metal sourcechemical, also referred to herein as the “metal compound,” is a halideand the adsorbed monolayer is terminated with halogen ligands. In someembodiments, the metal compound is selected from the group consisting ofmetal bromides, metal chlorides, and metal iodides. As an example, atantalum-containing metal carbide film can be deposited using a metalcompound selected from the group consisting of TaBr_(w), TaCl_(x), andTaI_(z), where w, x, y, and z are numbers from 1 to 5. In someembodiments, where a tantalum-carbide film is desired, TaCl₅ is used asthe metal compound.

Excess metal source material and reaction byproducts (if any) areremoved from the reaction space, e.g., by purging with an inert gas.Excess metal source material and any reaction byproducts may be removedwith the aid of a vacuum generated by a pumping system.

Maximum step coverage on the workpiece surface is typically obtainedwhen the metal source material forms no more than about a singlemonolayer in each self-limiting pulse. Due to the size of thechemisorbed species and the number of reactive sites, somewhat less thana monolayer may be deposited in each pulse of metal reactant. Thus, themaximum coverage of metal source material may be less than a monolayer.Depending on the process conditions in some embodiments it may bepossible that more than one monolayer of first reaction is found on thesubstrate surface.

In a second phase of the deposition cycle (“carbon-contributing phase”),a second reactant, also referred to herein as a “second sourcechemical”, is pulsed into the reaction space to react with themetal-containing molecules left on the substrate surface by thepreceding pulse. The second source chemical is an aluminum hydrocarboncompound. Preferably, in the second phase carbon is incorporated intothe film by the interaction of the second source chemical with themonolayer left by the metal source material. In preferred embodiments,reaction between the second source chemical and the chemisorbed metalspecies produces a metal carbide film over the substrate.

Aluminum may also be incorporated into the film in this second phase.Reaction conditions, including, without limitation, choice of reactant,temperature, pressure and pulse and purge times are adjusted to achievea desired aluminum content in the film. In some embodiments the aluminumcontent may vary from about 0% to about 30%, more preferably from about6% to about 16%. In other embodiments the aluminum content may behigher.

The aluminum hydrocarbon may be selected from the group consisting ofalkanes, alkenes and alkynes. For example, the carbon-containingcompound may be TMA, DMAH, or TEA. In some embodiments more than onealuminum hydrocarbon compound may be used. For example, two or morealuminum hydrocarbon compounds may be provided simultaneously in thesame pulse. In other embodiments two or more different aluminumhydrocarbon compounds are provided in distinct ALD cycles with a singledeposition process.

Excess second source chemical and reaction byproducts, if any, areremoved from the reaction space by a purging gas pulse and/or vacuumgenerated by a pumping system. Purging gas is preferably any inert gas,such as, without limitation, argon (Ar) or helium (He). A phase isgenerally considered to immediately follow another phase if a purge(i.e., purging gas pulse) or other reactant removal step intervenes.

Additional reactants may be utilized in some embodiments, for example toreduce the deposited film or to incorporate a further species in thefilm. In some embodiments a third reactant may be a reducing agent, suchas plasma-excited species of hydrogen generated by, e.g., an in situ orremote plasma generator. The reducing agent may be pulsed to thereaction space (or generated in the reaction space) after the metalphase and/or the carbon-contributing phase to reduce the deposited film.The reducing agent can be used, for example, to remove impurities, suchas halogen atoms or oxidizing material (e.g., oxygen atoms) in the filmand/or the substrate. It may also be used to control the incorporationof aluminum into the metal carbide film, thereby controlling theproperties of the film. In some embodiments, thermal ALD and plasma ALDcycles are used in the same deposition process to control aluminumconcentration in the deposited film. The ratio of thermal ALD cycles toplasma ALD cycles can be selected to achieve the desired aluminumconcentration and/or concentration profile in the thin film.

In some embodiments, plasma parameters can be selected to modify thelevel of incorporation of aluminum into the metal carbide film and/orratio of tantalum to carbon. That is, in some embodiments, filmcomposition can be controlled as a function of plasma parameters. Inaddition to composition, other film characteristics such ascrystallinity, crystal lattice constant, resistivity and crystal stresscan be adjusted by selecting appropriate plasma parameters.

In some embodiments, plasma parameters are selected from relationshipsthat have been established between plasma parameters and filmcomposition and characteristics. “Plasma parameters” may include, forexample, RF power and RF frequency. One plasma parameter, such as RFpower, or multiple plasma parameters, i.e., a set of plasma parameters,such as RF power and RF frequency may be adjusted in one or more ALDcycles to achieve the desired film properties. Plasma parameters arepreferably selected to yield a metal carbide film with a desiredcomposition. In some cases plasma parameters are selected to form a gateelectrode with a particular composition to yield a desired gate stackwork function.

In some embodiments, deposition recipes for metal carbide films aredetermined or designed by selecting plasma parameters. As an example,the RF power may be selected to affect a stoichiometry as desired. Asanother example, a particular plasma pulse duration or RF power on timecan be used to obtain a desired composition. As still another example,the desired composition may be achieved by selecting a combination of RFpower, reactant pulse duration, and reactant flow rate.

Preferably, the plasma-excited species comprises hydrogen.Plasma-excited species of hydrogen may include, without limitation,hydrogen radicals (H*) and hydrogen cations (e.g., H⁺, H₂ ⁺).Plasma-excited species of hydrogen may be formed in situ or remotely,for example from molecular hydrogen (H₂) or hydrogen-containingcompounds (e.g., silane, diborane, etc). In some embodiments, one ormore of the reactants described herein can be provided as a plasma.

Relationships between deposition parameters such as plasma, reactants,etc. and thin film composition can be established by selectingparameter(s) and depositing a metallic carbide film by a particularatomic layer deposition process using the selected parameter(s) until afilm of desired thickness is formed. The film composition andcharacteristics can then be determined and another film deposited usingdifferent parameters. This process can be repeated for differentparameters to develop relationships between the parameters and filmcomposition.

By selecting appropriate reaction conditions, a compound film with acomposition as desired can be formed.

In one embodiment, formation of a metal carbide film via an ALD-typeprocess comprises one or more deposition cycles, each comprising thesteps of:

1. providing a metal compound to the reaction space;

2. purging and/or evacuating excess metal compound and reactionbyproducts;

3. providing an aluminum hydrocarbon compound to the reaction space; and

4. purging and/or evacuating excess aluminum hydrocarbon compound andreaction byproducts from the reaction space.

Steps 1-4 can be referred to as a thermal ALD cycle. Steps 1-4 can berepeated as necessary to produce a metal carbide film of desiredthickness and with a desired aluminum concentration. For example, steps1-4 may be repeated up to 10, 100 or even 1000 or more times to producemetal carbide layers with uniform thicknesses ranging from one orseveral atomic layers to 100 nanometers (nm) or more. In someembodiments, steps 1-4 may be repeated until a metal carbide film isformed with a thickness of from about 1 to about 1000 Å, preferably lessthan about 1000 Å, more preferably less than about 500 Å. In someembodiments the film has a thickness of less than about 300 Å, and inother embodiments less than about 200 Å. In one embodiment, thethickness is preferably between about 100 Å and about 200 Å. In otherembodiments the thickness is preferably from about 20 to about 200 Å.The skilled artisan will appreciate that the thickness of the metalcarbide film can vary depending on the particular application. As anexample, for NMOS gate applications, the thickness is typically fromabout 50 Å to about 500 Å. As another example, for MIM capacitorapplications (e.g., DRAM, eDRAM, etc.) the thickness range is typicallyfrom about 50 Å to about 200 Å. Further, for applications in which themetal carbide thin film serves to set the work function in a flashmemory, the thickness is preferably between about 20 Å and about 200 Å.

In some embodiments, steps 1 and 2 are repeated a predetermined numberof times prior to steps 3 and 4. For example, steps 1 and 2 may berepeated five times prior to steps 3 and 4. As another example, steps 1and 2 may be repeated ten times prior to steps 3 and 4. It should beunderstood that if a metal carbide film with compositional uniformity isdesired, the number of times steps 1 and 2 are repeated should notexceed that which will prevent substantial carburization of the metalfilm. In one embodiment, the metal compound has a low decompositiontemperature and the number of times steps 1 and 2 are repeated does notexceed one.

As discussed herein, selection of hydrocarbon aluminum reactants can beused to achieve deposition of films with desired characteristics, suchas adhesion, resistivity, oxidation resistance and/or work function. Insome embodiments multiple aluminum hydrocarbon compounds are used. Inaddition, various reaction conditions can be manipulated to achieve thedesired film qualities and composition. These reaction conditionsinclude, but are not limited to, reaction temperature, source containertemperature, pressure, flow rate, plasma parameters and pulse and purgetimes.

In one embodiment, formation of a metal carbide film via an ALD-typeprocess comprises two or more deposition cycles, a first cyclecomprising the steps of:

1. providing a metal compound to the reaction space;

2. purging and/or evacuating excess metal compound and reactionbyproducts;

3. providing a first aluminum hydrocarbon compound to the reactionspace; and

4. purging and/or evacuating excess aluminum hydrocarbon compound andreaction byproducts from the reaction space.

and a second deposition cycle comprising the steps of:

5. providing a metal compound to the reaction space;

6. purging and/or evacuating excess metal compound and reactionbyproducts;

7. providing a second aluminum hydrocarbon compound to the reactionspace; and

8. purging and/or evacuating excess aluminum hydrocarbon compound andreaction byproducts from the reaction space.

The first and second cycles need not be consecutive and the ratio offirst cycles to second cycles can be selected to achieve the desiredcomposition.

In some embodiments, the deposition cycles can begin with any of thereactants. Preferably the first and second aluminum hydrocarboncompounds are different compounds. Preferably the first and secondaluminum hydrocarbon compounds comprise TMA, TEA, or DMAH. In someembodiments, the first aluminum hydrocarbon compound comprises TEA andthe second hydrocarbon compound comprises TMA. In some embodiments,multiple deposition cycles using TEA are performed followed by multipledeposition cycles using TMA.

In some embodiments, the ratios between the first aluminum hydrocarbonpulses and second hydrocarbon pulses are between about 1:100 and 100:1.Preferably the ratio between first and second aluminum hydrocarbonpulses is about 5:1 to about 1:5. In some embodiments the ratio betweenfirst and second aluminum hydrocarbon pulses is about 1:1.

In some embodiments plasma can be used during the deposition of themetal carbide film. In one embodiment, formation of a metal carbide filmvia an ALD-type process comprises one or more plasma ALD depositioncycles, each comprising the steps of:

1. providing a metal compound to the reaction space;

2. purging and/or evacuating excess metal compound and reactionbyproducts;

3. providing a first aluminum hydrocarbon compound to the reactionspace;

4. purging and/or evacuating excess aluminum hydrocarbon compound andreaction byproducts from the reaction space;

5. providing a plasma-excited species to the reaction space; and

6. purging and/or evacuating excess plasma source and reactionbyproducts from the reaction space.

Steps 1-6 can be referred to as the plasma deposition cycle. In someembodiments the plasma source can be provided after the metal compoundand before the aluminum hydrocarbon compound. In some embodiments, thedeposition cycle can begin with any of the reactants. Preferably, theplasma-excited species comprises hydrogen.

In some embodiments plasma ALD cycles and thermal ALD cycles are used inthe same deposition process. The ratio between the thermal ALD cyclesand plasma ALD cycles is typically between about 1:100 and 100:1.Preferably the ratio between first and second aluminum hydrocarbonpulses is about 5:1 to about 1:5. In some embodiments the ratio betweenthermal and plasma ALD cycles is about 1:1.

The following general conditions apply to any of the deposition cyclesdisclosed herein. The reaction temperature is preferably from about 150°C. to about 550° C., more preferably from about 300° C. to about 400° C.In some embodiments the reaction temperature is about 350° C. to 375° C.

The reaction pressure is from about 0.5 to about 10 torr. In someembodiments the pressure is about 2 to about 7 torr. The pressure ispreferably adjusted to achieve a desirable growth rate and acceptableuniformity.

In some embodiments the reactant vessel temperature can be selected toprovide films with a desired characteristic. In some embodiments, thehalide reactant vessel temperature is about 40° C. to about 80° C. Forexample, for the deposition of tantalum containing films using a TaCl₅as a metal precursor, the reactant vessel temperature may be from about45° C. to about 70° C., more preferably about 65° C.

The metal reactant pulse time is preferably from about 0.1 to about 20seconds, more preferably from about 1 to about 10 seconds.

The aluminum hydrocarbon compound pulse time is preferably from about0.1 to about 20 seconds, more preferably from about 0.5 to about 2seconds. In some embodiments TMA is used as the aluminum hydrocarbonreactant and a pulse time of longer than about 1 second is used, morepreferably about 2 seconds. In other embodiments TEA is used as thealuminum hydrocarbon reactant with a pulse time of about 1 second. Inother embodiments DMAH is used as the aluminum hydrocarbon reactant witha pulse time of about 1 second. In other embodiments, two or moredifferent aluminum hydrocarbon reactants can be used. In still otherembodiments longer pulse times may be used. In some embodiments longerpulse times can be used for the aluminum hydrocarbon compound to affectthe saturation of the compound on the substrate.

Purge times are generally from about 0.1 to about 10 seconds, morepreferably about 2 to about 8 seconds. In some embodiments a purge timeof about 6 seconds is used. However, in other embodiments longer purgetimes may be used. In some embodiments purge times are the same forpurging the metal reactant and the aluminum hydrocarbon reactant, whilein other embodiments the purge times are different for the differentreactants.

Flow rates are generally from about 100 to about 400 sccm for the inertpurge gas, such as Ar. The carrier flow for both metal precursors andaluminum hydrocarbons is preferably about 100 to about 400 sccm. Thecarrier gas is preferably an inert gas, such as Ar, and may be the sameas or different from the purge gas. The flow rates of the purge andcarrier gases can be determined based, in part, on the particularreactor, as will be appreciated by the skilled artisan.

With reference to FIG. 1, an exemplary embodiment for forming a metalcarbide film by an ALD-type process is illustrated. After initialsurface termination, if necessary, a first reactant or source materialis supplied or pulsed 10 to the substrate or workpiece. In accordancewith a preferred embodiment, the first reactant pulse comprises acarrier gas flow and a metal precursor, preferably a volatile halidecompound that is reactive with the workpiece surfaces of interest. Thehalide compound comprises a metal species that is to form part of themetal carbide film. Accordingly, a metal-containing species adsorbs uponthe workpiece surfaces. The first reactant pulse self-saturates theworkpiece surfaces such that any excess constituents of the firstreactant pulse do not further react with the monolayer formed by thisprocess. Self-saturation is due to ligands, such as halide tailsterminating the monolayer, protecting the layer from further reaction.In some embodiments the first reactant is a tantalum halide compound,such as TaCl₅.

Excess first reactant is then removed 20 from the reaction space.Preferably, step 104 merely entails stopping the flow of the firstreactant or chemistry while continuing to flow a carrier gas (e.g., Aror H₂) for a sufficient time to diffuse or purge excess reactants andreactant byproducts from the reaction space, preferably with greaterthan about two reaction chamber volumes of the purge gas, morepreferably with greater than about three chamber volumes. Preferably,the removal 20 comprises continuing to flow purge gas for between about0.1 seconds and 20 seconds after stopping the flow of the first reactantpulse. Inter-pulse purging is described in a co-pending U.S. patentapplication, having Ser. No. 09/392,371, filed Sep. 8, 1999 and entitledIMPROVED APPARATUS AND METHOD FOR GROWTH OF A THIN FILM, the disclosureof which is incorporated herein by reference. In other arrangements, thechamber may be pumped down between alternating chemistries. See, forexample, PCT publication number WO 96/17107, published Jun. 6, 1996,entitled METHOD AND APPARATUS FOR GROWING THIN FILMS, the disclosure ofwhich is incorporated herein by reference. Together, the adsorption 10and reactant removal 20 represent the first phase 50 in the depositioncycle. The first phase 50 in the illustrated deposition cycle is thusthe metal phase.

With continued reference to FIG. 1, a second reactant or source chemicalis pulsed 30 to the workpiece. The second chemistry reacts with oradsorbs upon the monolayer left by the first reactant. In someembodiments, the second reactant removes ligands from themetal-containing species deposited in step 10. In the illustratedembodiment, the second reactant is an aluminum hydrocarbon compound thatreacts with the layer deposited by the first reactant to form a metalcarbide. The aluminum hydrocarbon compound deposits carbon in the metallayer formed in the metal phase. In some embodiments, the aluminumhydrocarbon compound is pulsed with a carrier gas (e.g., H₂), preferablyan inert carrier gas (e.g., He, Ar).

After a time period sufficient to deposit carbon in the growing film,provision of the aluminum hydrocarbon compound is terminated andreaction byproducts (preferably also volatile), if any, are removed 40from the reaction space, preferably by a purge gas. The removal can beas described for step 20. Together, steps 30 and 40 represent a secondphase of the illustrated ALD process, which can also be referred to asthe carbon-contributing phase 60.

Steps 10-40 may be repeated 70 to form a metal carbide layer of adesired thickness. The repeat step 70 may be excluded if a metal carbidefilm with a thickness of about one monolayer or less is desired.

For the ALD-type processes describe herein, the substrate is preferablymaintained at a temperature from about 150° C. to about 550° C., morepreferably from about 350° C. to about 400° C. The chamber is preferablymaintained at a pressure from about 200 mTorr to about 10 Torr, morepreferably from about 1 Torr to about 8 Torr.

In some embodiments, the first reactant is a tantalum halide, such asTaCl₅, the second reactant is an aluminum hydrocarbon compound such asTMA, DMAH, or TEA, and the film being formed is a tantalum carbide. Thetantalum carbide film preferably comprises aluminum. In some embodimentsthe tantalum carbide film comprises from about 6 to about 16% aluminum.

In some embodiments, the film can be annealed after deposition.Annealing the film after deposition can modify the properties of thethin film. For example, annealing can modify the hydrogen and chlorinecontent of the film. Preferably, during annealing the substratetemperature is about 500° C. to about 1200° C. In some embodiments, thesubstrate temperature during the annealing step is about 600° C. toabout 1000° C. Preferably, the annealing step is carried out in an inertatmosphere. Preferred inert atmospheres for annealing comprise nitrogen,helium, and argon. Preferably the pressure is around atmosphericpressure during the annealing step. In some embodiments, the pressurecan be above or below atmospheric pressure. In some embodiments, theannealing atmosphere comprises a low oxygen partial pressure.

Flash Memory

In some embodiments flash memory structures are provided in which ametal carbide film is deposited by ALD as described herein to form atleast a part of the control gate. The main elements of an exemplaryflash memory structure are illustrated in FIG. 2. A dielectric layer(tunnel oxide) 110 is deposited over a substrate 100. The dielectriclayer 110 typically SiO₂, although in some embodiments it may be ahigh-k material. High k materials are generally forms of metallic oxideswith k values greater than about 7, such as aluminum oxide (Al₂O₃),zirconium oxide (ZrO₂), hafnium oxide (HfO₂), tantalum oxide (Ta₂O₅),barium strontium titanate (BST), strontium bismuth tantalate (SBT),lanthanide oxides, and combinations thereof, such as HfSiO_(x) andHfZrO_(x). Although typically an oxide, the dielectric layer 110 may beanother type of material.

A floating gate 120 is deposited directly over the dielectric layer. Thefloating gate 120 may comprise, for example, polysilicon. In someembodiments the floating gate 120 is replaced with a charge trap layer.In some embodiments the charge trap layer is silicon nitride, althoughother materials are possible.

A barrier oxide (or blocking dielectric) 130 is formed over the floatinggate or charge trap layer 120. In some embodiments the barrier oxide 130comprises Al₂O₃, although other materials such as AlLaO_(x), AlZrO_(x)and HfLaO can be used. The barrier oxide 130 may also be, for example,an ONO (oxide nitride oxide) structure comprising a bottom dielectricmaterial adjacent to the floating gate or charge trap layer 120, a topdielectric material adjacent to the overlying control gate 140 and anintervening nitride layer located between the top and bottom dielectricmaterial.

A control gate 140 is formed over the barrier oxide. Forming controlgate 140 preferably comprises depositing a metal carbide gate electrodelayer 150 by ALD using one or more aluminum hydrocarbon compounds, suchthat the metal carbide layer controls the work function of the controlgate 140. In preferred embodiments the metal carbide is TaC. The metalcarbide layer 150 is preferably deposited to a thickness of about 100 to200 Å. The deposition conditions, for example temperature, pressure,pulse and purge times, plasma conditions (if used) and reactant choiceare adjusted to achieve a desired amount of aluminum in the metalcarbide layer 150 and thus produce the desired work function. Inaddition, the aluminum content is preferably such that the film is ableto self-passivate during subsequent patterning and/or deposition steps.

In some embodiments the metal carbide layer serves as the entire controlgate. In other embodiments, a second upper gate electrode layer 160 isdeposited over and adjacent to the first lower gate electrode layer 150.The second gate electrode layer 160 comprises a conductive material,such as polysilicon, titanium nitride and/or a metal, such as tungsten.The upper gate electrode layer 160 may be thicker than the lower gateelectrode layer 150. In some embodiments the upper gate electrode layer160 has a thickness of about 1000 Å. Typically, the upper gate electrodelayer 160 does not contribute to the work function of the control gate140. However, in some embodiments the thickness of the lower gateelectrode layer 150 and the upper gate electrode layer 160 are selectedso that each contributes to the work function such that a desired workfunction is achieved.

Suitable materials for the dielectric layer 110, the floating gate orcharge trap layer 120, the barrier oxide 130 and upper gate electrodelayer 160 (if present) are known in the art and may be selected by theskilled artisan based on the particular circumstances. The dielectriclayer 110 can be deposited by any deposition method know in the art,such as ALD or PEALD. The upper gate electrode layer 160 is preferablydeposited by a chemical vapor deposition (CVD) type or physical vapordeposition (PVD) type process. In some embodiments the barrier oxide 130and the control gate 150 are deposited on the same platform without anyair break.

The structure is then patterned, etched and passivated, for example withsilicon oxide. During the passivation process, the edges of the metalcarbide layer are exposed and the aluminum in the metal carbide reactswith oxygen to self-passivate the remaining metal film.

Gate Electrodes

In some embodiments transistor structures are provided in which a metalcarbide film is deposited by ALD as described herein and forms at leasta part of the gate electrode. A schematic illustration of a gate stackin a CMOS transistor is provided in FIG. 3. In particular, asemiconductor substrate 200 is shown with a transistor gate stack 210formed thereover. In the illustrated embodiment, the substrate 200comprises an upper portion of a single-crystal silicon wafer, though theskilled artisan will appreciate that the substrate can also compriseother semiconductor materials. The gate stack 210 includes a gateelectrode layer 220 comprising metal carbide. Sidewall spacers 230 andan insulating layer 240 protect and isolate the electrode 220 in aconventional manner. Also illustrated is a more highly conductivestrapping layer 250, typically including metal, over thesilicon-containing gate electrode layer 220. The strap 250 facilitatesrapid signal propagation among transistor gates across the wafer,connecting the gates to logic circuits. Note that integrated circuittransistors can have a variety of forms that do not all resemble that ofFIG. 3. The gate electrode layer 220 of the preferred embodiments,however, will have application to gate electrodes in a variety oftransistor types (e.g., heterojunction BiCMOS transistors).

At least a portion of the gate electrode 220 is formed by depositing ametal carbide layer by ALD using one or more aluminum hydrocarboncompounds. In some embodiments the metal carbide layer controls the workfunction of the gate electrode 220. In preferred embodiments the metalcarbide comprises TaC. The metal carbide layer is preferably depositedto a thickness of about 20 to 200 Å. The deposition conditions, forexample temperature, pressure, pulse and purge times, plasma conditions(if used) and reactant choice are adjusted to achieve a desired amountof aluminum in the metal carbide layer and thus produce the desired workfunction. In addition, the aluminum content is preferably such that thefilm is able to self-passivate during subsequent patterning and/ordeposition steps.

In some embodiments the metal carbide layer serves as the entire gateelectrode 220. In other embodiments, a second upper gate electrode layeris deposited over and adjacent to the metal carbide layer. The secondupper gate electrode layer comprises a conductive material, such aspolysilicon, titanium nitride and/or a metal, such as tungsten. Theupper gate electrode layer may be thicker than the metal carbide gateelectrode layer. In some embodiments the upper gate electrode layer hasa thickness of about 1000 Å. Typically, the upper gate electrode layerdoes not contribute to the work function of the gate electrode. However,in some embodiments the thickness of the lower gate electrode layer andthe upper gate electrode layer are selected so that each contributes tothe work function such that a desired work function is achieved. Theupper gate electrode layer is preferably deposited by a chemical vapordeposition (CVD) type or physical vapor deposition (PVD) type process.

EXAMPLES

Tantalum carbide films were deposited on silicon dioxide (SiO₂), Al₂O₃,SiN, HfO₂ and Ta₂O₅ substrates by ALD-type processes in both EmerALD andPulsar reactors. The sequence of steps in the processes includedalternately and sequentially pulsing a metal compound (TaCl₅), analuminum hydrocarbon (TMA or TEA) and a purge gas (Ar) into a reactionspace containing the substrate. Deposition was conducted under a varietyof reaction conditions.

The sequence of gas pulses was as follows:

(1) TaCl₅ pulse;

(2) Ar purge;

(3) TMA or TEA pulse; and

(4) Ar purge.

Steps (1)-(4) were repeated to form tantalum carbide films.

Tantalum Carbide Deposition Using TMA

In one experiment, tantalum carbide films were deposited on silicondioxide (SiO₂) from TMA and TaCl₅ at a reaction temperature of about375° C. The sequence of gas pulses and purges (milliseconds, “ms”) wereas follows:

(1) TaCl₅ pulse (1000 ms);

(2) Ar purge (3000 ms);

(3) TMA pulse (1000 ms); and

(4) Ar purge (3000 ms).

Steps (1)-(4) were repeated to form a uniform tantalum carbide film witha deposition rate of approximately 3.5 Å/cycle.

Tantalum Carbide Deposition Using TEA

In another experiment, tantalum carbide films were deposited on silicondioxide (SiO₂) from TEA and TaCl₅ at a reaction temperature of about375° C. The sequence of gas pulses and purges (milliseconds, “ms”) wereas follows:

(1) TaCl₅ pulse (1000 ms);

(2) Ar purge (3000 ms);

(3) TEA pulse (2000 ms); and

(4) Ar purge (4000 ms).

Steps (1)-(4) were repeated to form a uniform tantalum carbide film witha deposition rate of approximately 4 Å/cycle.

TaC Film Properties

The resistivity of a 200 Å tantalum carbide film formed according to theprocedure outlined in the examples above was about 1200 uohm*cm when TMAwas used as the aluminum hydrocarbon and about 700 uohm*cm when TEA wasused as the aluminum hydrocarbon reactant.

When deposited on an Al₂O₃ substrate, a TaC film deposited using TMA asthe aluminum hydrocarbon compound delaminated from the substrate inscratch and tape tests. However, a TaC film deposited using TEA underotherwise identical conditions showed good adhesion using the samemeasures.

In at least some of the aforesaid embodiments, any element used in anembodiment can interchangeably be used in another embodiment unless sucha replacement is not feasible.

It will be appreciated by those skilled in the art that various otheromissions, additions and modifications may be made to the methods andstructures described above without departing from the scope of theinvention. All such modifications and changes are intended to fallwithin the scope of the invention, as defined by the appended claims.

We claim:
 1. A thermal atomic layer deposition (ALD) process for forminga metal carbide thin film comprising Ti or Ta on a substrate in areaction space, the process comprising alternately and sequentiallycontacting the substrate with vapor phase pulses of a metal halide andtriethyl aluminum (TEA), wherein the metal halide is a tantalum halideor titanium halide, such that a metal carbide film comprising Ti or Taand at least about 16% aluminum is formed.
 2. The process of claim 1,wherein contacting the substrate with vapor phase pulses of a metalhalide and TEA comprises: providing the metal halide to the reactionspace, thereby forming a metal layer over the substrate; removing vaporphase metal halide from the reaction space; providing vapor phase TEA tothe reaction space, wherein TEA reacts with the metal layer to (a)deposit carbon in the metal layer and (b) form volatile reactionbyproducts; and removing the vapor phase TEA and the volatile reactionbyproducts from the reaction space.
 3. The process of claim 2, whereinthe TEA provides carbon to the metal layer to form a metal carbide. 4.The process of claim 1, wherein the metal halide comprises Ti.
 5. Theprocess of claim 1, wherein the metal halide comprises Ta.
 6. Theprocess of claim 1, wherein the metal halide is selected from the groupconsisting of group consisting of TaBr_(w), TaCl_(x), and TaI_(z),wherein w, x, y, and z are integers from 1 to
 5. 7. The process of claim1, wherein the metal halide comprises TaCl₅.
 8. The process of claim 1,wherein the metal carbide film comprises about 30% aluminum.
 9. Theprocess of claim 1, wherein providing the TEA to the reaction spacecomprises a TEA pulse of up to about 20 seconds.
 10. The process ofclaim 1, wherein providing the metal halide to the reaction spacecomprises a metal halide pulse of about 1 to 10 seconds.
 11. The processof claim 1, wherein the substrate has a temperature of about 350° C. to400° C.
 12. The process of claim 1, wherein the metal carbide film isdeposited to a thickness of about 1 to about 1000 Å.
 13. The process ofclaim 1, wherein the metal carbide film is deposited to a thickness ofabout 100 to about 200 Å.